4. Strong collision: given a message M1, it is not possible to find two distinct messages such that h (M1’) = h (M1). The probability of this collision is 2n/2.
Hash function is used in message authentication which uses a secret code before hashing so that no one else can modify the message and hash and then can encrypt the message for confidentiality. There are several ways of applying hash for message authentication:
1. One is to apply hash to the message and encrypt it and decrypt it using the same key.
2. Hash is applied to the message and encrypted now the encrypted hashed message and message is sent to the receiver and the receiver decrypts it using the same key
3. Hash is applied to the message and encrypted using the sender’s public key now the encrypted hashed encrypted message and the message is
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Secret code is applied to the message and hashed and is sent to the receiver
6. Secret code is applied to the message and hashed and this hashed message is encrypted and sent to the receiver.
It is used in digital signatures the hash is encrypted using sender’s private key and then encrypted using public key and sent to the receiver and the receiver decrypts the message using the private key. It is used in password storage A good system does not store the plaintext equivalent but store something else which include some randomness .so now if we use hash and because of its onewayness it is impossible to get back the password. If we use pure hash in the password and encrypt it, it can be broken easily by exhaustive search so that is why we have add some randomness to the password before the hash function is applied. The randomness is stored with the password hash. So now instead of pure hash and pure password we store the hash o/p of password chosen by me and some random number chosen by the system. From now whenever we use the password the system associates with the random number and gives access. This is how a hash is used in password storage.
Functions of